Lightning protection systems are typically integrated into wind turbine blades to address the problem of lightning strikes. An electrically conductive lightning receptor is arranged on or adjacent an outer surface of the blade to receive lightning that strikes the blade. Typically, the lightning receptor is electrically connected to a down cable that extends inside the blade. The lightning is discharged from the lightning receptor to the down cable and then to a ground potential via conductors that extend inside the blade, nacelle and tower of the wind turbine. Lightning protection systems therefore allow lightning to be discharged safely and minimise the risk of damage to the wind turbine from lightning strikes.
For example, US 2011/0182731 describes a wind turbine blade in which receptors extend through the blade shell such that they are exposed at the outer and inner surfaces of the blade shell. At the inner surface of the blade shell, the receptor is connected to a down cable. To increase the effectiveness of the lightning protection system, a conducting layer is laid over the outer surface of the blade shell and hence over the lightning receptors. The conducting layer increases the area of the blade that can receive lightning, thereby increasing the rate at which the receptors capture lightning strikes.
However, such wind turbine blades are cumbersome to manufacture because the conducting layer must be added to the blade after the blade shell has been manufactured, which requires an extra, time-consuming step in the manufacturing process. Furthermore, ridges or other such discontinuities of the outer blade surface in the region of the lightning receptors can adversely affect the aerodynamic design of the blade, leading to reduced aerodynamic efficiency.
It is an object of the invention to mitigate or overcome these problems.